This invention relates to line mounted apparatus for measuring line potential. More particularly, this invention relates to the measurement of high power, alternating current (AC), transmission line voltages. This invention employs power line mounted, radio transmitting, electrically isolated modules. Preferably, the modules are mounted on all power conductors connected to the load to be monitored.
Each module contains apparatus for measuring the instantaneous voltage associated with the power conductor upon which the module is installed. The measured instantaneous voltage is derived from the potential difference induced by the electric field associated with the power line upon the outer toroidal structure of the module.
The novel voltage measuring apparatus disclosed herein makes possible the use of the module as a hot stick mounted power line voltage probe.
High power, AC, transmission line potentials have been typically measured by the use of step down isolation voltage transformers where one end of the primary high voltage winding was conductively coupled to the high voltage line. The existence of a direct conductive link between the high voltage passing through the power line and ground typically exposed the voltage measuring equipment to high voltage stresses especially when hit by lightning strikes. The continual exposure to such high voltage stresses necessitated bulky and therefore expensive construction of such voltage measuring equipment to assure reliable operation and operator safety over extended periods of time.
It is desirable to measure potential values along the power line for short periods or continually at arbitrary positions. This measured voltage can be used to derive Fourier frequency components, power, and power factor information associated for the operation of the power line being measured, and to locate and diagnose anomalies in the use and transmission of electric power.
Various power line sensors have been disclosed in the prior art. For example see U.S. Pat. Nos. 3,438,896, 3,633,191, 4,158,810 and 4,268,818. It has been proposed to use sensors of this type and of the greatly improved form disclosed in U.S. Pat. No. 4,384,289 for dynamic line rating of electrical power transmission lines. An improved line voltage sensor was disclosed in the above-identified application Ser. No. 484,681, now U.S. Pat. No. 4,689,752. Specifically, line voltage was derived from the ratio of voltages between two series capacitors; one formed by the internal structure of the module while the second was formed between the outer skin of the module and ground. However, the former capacitance was found to change value due to the influence of conductive debris on the structure forming the capacitor, and the proximity of high voltage gradients associated with the power line. This change can alter the value of the ratio of the two capacitances and degrade the accuracy of the voltage measurement.
It is therefore an object of the invention to provide apparatus for measuring the instantaneous potential difference between ground and a power line conductor.
Another object of the invention is to provide apparatus of the above character which is hot stick mounted.
A further object of the invention is to provide apparatus of the above character capable of transmitting measurements to ground.
Still another object of the invention is to provide apparatus of the above character which may be left on the power conductor for an indefinite time.
Yet another object of the invention is to provide apparatus of the above character that is not subject to error caused by varying weather conditions.